The get-a-life fans of “Mad Men” — including “NBC Nightly News” anchor Brian Williams — have taken to the Internet to point out inaccuracies in the series that prides itself on getting all the details right when it comes to hair and wardrobe, props, dialogue and history.

This week, on his blog The Daily Nightly, Williams took a sharp turn from his usual subject matter — his own news show — to outline a list of boo-boos that series creator Matthew Weiner made in last Sunday night’s Season 4 premiere, which takes place in November 1964.

* Don Draper, the character played by Jon Hamm, could not have been watching a black-and-white NFL game late at night on TV. “Questionable,” as the anchor politely puts it. Prime-time football didn’t start until 1970, with the first “Monday Night Football” game.And a slow-motion replay? Not in ’64, says the anchor.

* A young copywriter, Joey Baird (Matt Long), is dressed in a sweater vest. Williams points out that the sweater vest wasn’t commonly worn until 1967-70, at least three years after the period covered in the show’s fourth season.

The anchorman acknowledges that finding fault with the show’s period details has become a “small industry” on the Web.

Indeed, there are sites devoted to the veracity of the dialogue on “Mad Men” and another on “Mad Men Anachronisms,” in which geeky viewers debate whether people were still allowed to smoke on commuter trains in the early 1960s the way Don does. (They were.)

Turns out the producers originally wanted to show Don viewing a hockey game between the New York Rangers and the Toronto Maple Leafs, but couldn’t get rights, according to a report yesterday in the Los Angeles Times.

Instead, producers substituted audio of a football game, thinking it would blend into the background.